Novas hybrid positioning technology using terrestrial digital broadcasting signal (DBS) and global positioning system (GPS) satellite signal

ABSTRACT

A positioning method using global positioning system (GPS) signal and digital broadcasting system (DBS) signal. The method includes detecting a presence status of the GPS signal through a signal detector in a receiver, detecting a presence status of the DBS signal through the signal detector, determining the signal strength of the GPS signal if the GPS signal is detected, determining the signal strength of the DBS signal if the DBS signal is detected, choosing one positioning mode among a plurality of positioning modes in a signal processing unit in the receiver based on signal presence status and the signal strength of a detected signal, and determining a location of the receiver based on the chosen positioning mode. The plurality of positioning modes includes stand-alone GPS mode, assisted GPS (AGPS) mode, assisted GPS positioning with DBS assist mode, DBS positioning with GPS assist mode, stand-alone DBS mode, and assist DBS mode.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/736,725, A NOVAS HYBRID POSITIONING TECHNOLOGY USING TERRESTRIALDIGITAL BROADCASTING SIGNAL (DBS) AND GLOBAL POSITIONING SYSTEM (GPS)SATELLITE SIGNAL, filed on Nov. 15, 2005, the specification of which ishereby incorporated in its entirety by this reference.

FIELD OF THE INVENTION

The present invention relates to positioning technology and moreparticularly to positioning technology using terrestrial digitalbroadcasting signal (DBS) and global positioning system (GPS) satellitesignal.

BACKGROUND OF THE INVENTION

Global positioning system (GPS) is currently the most widely usedpositioning system. Usually, the GPS satellites are located more than 20kilometers above the surface of earth. GPS signal degrades significantlyover such a long distance when it reaches the earth. Generally, a GPSreceiver requires at least a sensibility of −130 dBm to acquire a GPSsignal in a clear and open sky environment. In urban or indoorenvironment, the GPS receiver may require a sensitivity parameterranging from −155 dBm to −160 dBm or more than −160 dBm to perform GPSpositioning functions. Furthermore, the performance and accuracy of GPSpositioning system will degrade dramatically due to any reflection,blockage and multi-path effect of GPS signals under urban or indoorenvironment.

With the digitalization of terrestrial analog audio broadcasting andanalog video broadcasting technologies, which correspond to twomainstream standards, namely DAB (digital audio broadcasting) and DVB(digital video broadcasting)/ATSC (advanced television system committee)respectively, terrestrial digital broadcasting system (T-DBS), whichincludes DAB, DVB, and ATSC system, has an unparalleled edge over theglobal positioning system in terms of signal transmission power, signaltransmission distance. Furthermore, the penetration ability of T-DBSsignals is much stronger than that of GPS signal broadcasting at L1carrier frequency level. Terrestrial digital broadcasting system can beused in environments such as basement, stair ways and undergroundparking lots where GPS positioning fails to perform. In addition, theuse of the terrestrial digital broadcasting system can serve as acomplement to the GPS in an urban environment where GPS positioningresults become unreliable due to the densely built high-rises. Thus, itis to a hybrid positioning technology using T-DBS signal and GPS signalthat the present invention is primarily directed.

SUMMARY OF THE INVENTION

There is provided a receiver for determining position using terrestrialdigital broadcasting signal (DBS) and global positioning system (GPS)satellite signal. The receiver includes a first tuner, a second tuner, asignal detector, a hybrid signal processing unit, a measurement dataprocessing unit and an assist data processing unit. The first tuner isused to convert the GPS signal from its original frequency to anintermediate frequency (IF). The second tuner is used for converting theDBS signal to an intermediate frequency (IF). The signal detector iscapable of detecting the existence of the GPS signal and the DBS signal,measuring the signal strength of the detected signal and outputting asignal indicating a positioning mode based on the measured signalstrength. The hybrid signal processing unit is capable of choosing apositioning mode among a plurality of positioning modes and determiningposition of the transmitters and arrival time difference between eachsignal arriving at the receiver. The measurement data processing unitcoupled to the hybrid signal processing unit for determining theposition of the receiver based on the position of the transmitters andthe arrival time difference. The assist data processing unit coupled tothe hybrid signal processing unit is adapted to receive assistance datafrom an assist station and provide the assistance data to hybrid signalprocessing unit for further signal processing when an assist positioningmode is chosen. The plurality of positioning modes includes stand-aloneGPS positioning mode, assisted GPS (AGPS) positioning mode, assisted GPSpositioning with DBS assist mode, DBS positioning with GPS assist mode,stand-alone DBS positioning mode, and assist DBS positioning mode.

There is also provided a method for obtaining a position using globalpositioning system (GPS) signal and digital broadcasting system (DBS)signal. The method includes detecting the presence of a GPS signal in asignal detector in a receiver, detecting the presence of a DBS signal inthe signal detector, determining the signal strength of the GPS signalif the GPS signal is detected, determining the signal strength of theDBS signal if the DBS signal is detected, providing a plurality ofpositioning modes, choosing one positioning mode among the plurality ofpositioning modes in a signal processing unit in the receiver based onsignal presence status and the signal strength of the detected signal,and determining the location of the receiver based on the chosenpositioning mode. The plurality of positioning modes includesstand-alone GPS positioning mode, assisted GPS (AGPS) positioning mode,assisted GPS positioning with DBS assist mode, DBS positioning with GPSassist mode, stand-alone DBS positioning mode, and assist DBSpositioning mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be apparent from the followingdetailed description of exemplary embodiments thereof, which descriptionshould be considered in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a simplified model of a positioning system;

FIG. 2 is a schematic diagram of a hybrid positioning system using GPSand/or DBS signal according to one embodiment of the present invention;

FIG. 3 is a block diagram of an exemplary GPS/DBS receiver according toone embodiment of the present invention;

FIG. 4 is a transmission frame of a DAB signal according to oneexemplary embodiment of the invention;

FIG. 5 is a detailed format of a transmission frame of a DAB signal inMode-I according to one exemplary embodiment of the invention;

FIG. 6 is a mega-frame initialization packet in a mega frame of a DVBsignal according to one exemplary embodiment of the invention;

FIG. 7 is a frame of an ATSV signal according to one exemplaryembodiment of the invention; and

FIG. 8 is a flowchart illustrating a positioning method using GPS andDBS signal according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a simplified model of a positioning system. Theposition system includes a plurality of wireless transmission station(e.g. 102, 104, 106, 108)), a receiving station such as a mobilereceiver 110 and an optional reference station 112 (also known as assistserver, assist station, or fixed monitor). For a GPS system, in order tocalculate the user position, a receiver generally needs positionalinformation from at least four different transmission stations. Forsimplicity, FIG. 1 illustrates four transmission stations S0 102, S1104, S2 106 and S3 108 containing corresponding location information(x0, y0, z0), (x1, y1, z1), (x2, y2, z2), and (x3, y3, z3). Coordinatesof the four transmission stations, mobile receiver and the referencestation are shown in FIG. 1. According to the spatial coordinateformula, the following equation group (1) can be obtained:$\begin{matrix}\{ {\begin{matrix}{\sqrt{( {x_{0} - x} )^{2} + ( {y_{0} - y} )^{2} + ( {z_{0} - z} )^{2}} = {c \times ( \tau_{c\quad d\quad 0} )}} \\{\sqrt{( {x_{1} - x} )^{2} + ( {y_{1} - y} )^{2} + ( {z_{1} - z} )^{2}} = {c \times ( \tau_{c\quad d\quad 1} )}} \\{\sqrt{( {x_{2} - x} )^{2} + ( {y_{2} - y} )^{2} + ( {z_{2} - z} )^{2}} = {c \times ( \tau_{c\quad d\quad 2} )}} \\{\sqrt{( {x_{3} - x} )^{2} + ( {y_{3} - y} )^{2} + ( {z_{3} - z} )^{2}} = {c \times ( \tau_{c\quad d\quad 3} )}}\end{matrix}\quad}  & (1)\end{matrix}$, where τ_(cdi) is defined as the transmission time of a wireless signal(e.g. GPS signal or T-DBS signal) transmitted from a transmissionstation to a receiver.

Suppose that t_(jm) (m ∈ [0,3]) refers to the moment when the wirelesssignal is transmitted, and t_(in) (n ∈ [0,3] ) refers to the moment whenthe wireless signal reaches the receiver, then the following equationgroup (2) can be obtained:Receiver $\begin{matrix}\{ {\begin{matrix}{\sqrt{( {x_{0} - x} )^{2} + ( {y_{0} - y} )^{2} + ( {z_{0} - z} )^{2}} = {c \times ( {t_{j\quad 0} - t_{i\quad 0}} )}} \\{\sqrt{( {x_{1} - x} )^{2} + ( {y_{1} - y} )^{2} + ( {z_{1} - z} )^{2}} = {c \times ( {\tau_{j\quad 1} - t_{i\quad 1}} )}} \\{\sqrt{( {x_{2} - x} )^{2} + ( {y_{2} - y} )^{2} + ( {z_{2} - z} )^{2}} = {c \times ( {\tau_{j\quad 2} - t_{i\quad 2}} )}} \\{\sqrt{( {x_{3} - x} )^{2} + ( {y_{3} - y} )^{2} + ( {z_{3} - z} )^{2}} = {c \times ( {\tau_{j\quad 3} - t_{i\quad 3}} )}}\end{matrix}{\quad\{ {\begin{matrix}{{c \times ( {t_{j\quad 0} - t_{i\quad 0}} )} = {{c \times ( {t_{j\quad 0} + 0 - t_{i\quad 0}} )} = {c \times ( {t_{j\quad 0} + 0 - ( {t_{i\quad 0} + 0} )} )}}} \\{{c \times ( {\tau_{j\quad 1} - t_{i\quad 1}} )} = {{c \times ( {t_{j\quad 0} + {\Delta\quad T_{1}} - t_{i\quad 1}} )} = {c \times ( {t_{j\quad 0} + {\Delta\quad T_{1}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 1}}} )} )}}} \\{{c \times ( {\tau_{j\quad 2} - t_{i\quad 2}} )} = {{c \times ( {t_{j\quad 0} + {\Delta\quad T_{2}} - t_{i\quad 2}} )} = {c \times ( {t_{j\quad 0} + {\Delta\quad T_{2}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 2}}} )} )}}} \\{{c \times ( {\tau_{j\quad 3} - t_{i\quad 3}} )} = {{c \times ( {t_{j\quad 0} + {\Delta\quad T_{3}} - t_{i\quad 3}} )} = {c \times ( {t_{j\quad 0} + {\Delta\quad T_{3}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 3}}} )} )}}}\end{matrix}\{ \begin{matrix}{\sqrt{( {x_{0} - x} )^{2} + ( {y_{0} - y} )^{2} + ( {z_{0} - z} )^{2}} = {c \times ( {t_{j\quad 0} + 0 - ( {t_{i\quad 0} + 0} )} )}} \\{\sqrt{( {x_{1} - x} )^{2} + ( {y_{1} - y} )^{2} + ( {z_{1} - z} )^{2}} = {c \times ( {t_{j\quad 0} + {\Delta\quad T_{1}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 1}}} )} )}} \\{\sqrt{( {x_{2} - x} )^{2} + ( {y_{2} - y} )^{2} + ( {z_{2} - z} )^{2}} = {c \times ( {t_{j\quad 0} + {\Delta\quad T_{2}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 2}}} )} )}} \\{\sqrt{( {x_{3} - x} )^{2} + ( {y_{3} - y} )^{2} + ( {z_{3} - z} )^{2}} = {c \times ( {t_{j\quad 0} + {\Delta\quad T_{3}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 3}}} )} )}}\end{matrix} } }}  & (2)\end{matrix}$, where t_(j0)-t_(i0) is the transmission time for a wireless signaltraveling from a designated transmission station (S0) to the receiver.ΔT_(i) is the transmission time difference between transmission stationi and the designated reference transmission station; and 3) ΔT_(xi) isthe difference between the time when the signal transmitted from thetransmission station i reaches the receiver and the time when the signaltransmitted from the designated reference transmission station reachesthe receiver. Let M=t_(j0)−t_(i0), equation group (3) can be obtainedbased on equation group (2):Receiver $\begin{matrix}\{ \begin{matrix}{\sqrt{( {x_{0} - x} )^{2} + ( {y_{0} - y} )^{2} + ( {z_{0} - z} )^{2}} = {c \times (M)}} \\{\sqrt{( {x_{1} - x} )^{2} + ( {y_{1} - y} )^{2} + ( {z_{1} - z} )^{2}} = {c \times ( {M + {\Delta\quad T_{1}} - {\Delta\quad T_{x\quad 1}}} )}} \\{\sqrt{( {x_{2} - x} )^{2} + ( {y_{2} - y} )^{2} + ( {z_{2} - z} )^{2}} = {c \times ( {M + {\Delta\quad T_{2}} - {\Delta\quad T_{x\quad 2}}} )}} \\{\sqrt{( {x_{3} - x} )^{2} + ( {y_{3} - y} )^{2} + ( {z_{3} - z} )^{2}} = {c \times ( {M + {\Delta\quad T_{3}} - {\Delta\quad T_{x\quad 3}}} )}}\end{matrix}  & (3)\end{matrix}$

As illustrated in equation group (3), if (x0, y0, z0), (x1, y1, z1),(x2, y2, z2), (x3, y3, z3), ΔT_(i), and ΔT_(xi) are known, (x, y, z) andM can be determined, thereby, the user position can be calculated. Inother words, for a positioning system (GPS or T-DBS), if the differencein time of transmitting the wireless signal (ΔT_(i)) and the differencesin time of receiving the wireless signals (ΔT_(xi)) are known, and thepositions of each transmission stations are also known according to thereceived signals or local data base, the absolute location of thereceiver can be determined.

For the GPS system, usually, all GPS signals transmit at almost the sametime (all satellites transmit the same frame of signals simultaneously,while in fact, the transmission time may differ slightly with oneanother, but the receiver can correct the differences according tosatellite ephemeris), that is, ΔT_(i)≅0 (i ∈ [0,3]). Therefore, inreality, the three-dimension positioning can be performed simply basedon the differences in time of receipts of GPS signals at the receiverand the received navigation data contained in the GPS signal accordingto the equation group (3).

For terrestrial digital broadcasting system, if a single frequencynetwork (SFN) is set up, and if the network side can ensure alltransmission towers to transmit the same frame of signals simultaneously(transmission towers may be synchronized using GPS time), then the userposition may be determined after receiving signals transmitted by thetransmission towers according to the same positioning principle of theGPS system as shown in the equation group (3). If the network side failsto transmit signals simultaneously, or there is a difference in the timefor transmitting the signals from each transmission station, thedifference will lead to an error in positioning. If a high positioningaccuracy is desired, a reference station (also known as a fixed monitor)may be required to provide information for calculating ΔT_(i)(i ∈ [0,3])as illustrated in FIG. 1. ΔT_(i) can be calculated according to theequation group (4) shown below:

REFERENCE

$\begin{matrix}\{ \begin{matrix}{\sqrt{( {x_{0} - x_{f}} )^{2} + ( {y_{0} - y_{f}} )^{2} + ( {z_{0} - z_{f}} )^{2}} = {{c \times ( {t_{{jf}\quad 0} - t_{i\quad 0}} )} = {c \times ( {t_{{jf}\quad 0} - ( {t_{i\quad 0} + 0} )} )}}} \\{\sqrt{( {x_{1} - x_{f}} )^{2} + ( {y_{1} - y_{f}} )^{2} + ( {z_{1} - z_{f}} )^{2}} = {{c \times ( {\tau_{{jf}\quad 1} - t_{i\quad 1}} )} = {c \times ( {t_{{jf}\quad 0} + {\Delta\quad T_{1}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 1}}} )} )}}} \\{\sqrt{( {x_{2} - x_{f}} )^{2} + ( {y_{2} - y_{f}} )^{2} + ( {z_{2} - z_{f}} )^{2}} = {{c \times ( {\tau_{{jf}\quad 2} - t_{i\quad 2}} )} = {c \times ( {t_{{jf}\quad 0} + {\Delta\quad T_{2}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 2}}} )} )}}} \\{\sqrt{( {x_{3} - x_{f}} )^{2} + ( {y_{3} - y_{f}} )^{2} + ( {z_{3} - z_{f}} )^{2}} = {{c \times ( {\tau_{{jf}\quad 3} - t_{i\quad 3}} )} = {c \times ( {t_{{jf}\quad 0} + {\Delta\quad T_{3}} - ( {t_{i\quad 0} + {\Delta\quad T_{x\quad 3}}} )} )}}}\end{matrix}\quad  & (4)\end{matrix}$

where (x_(f),y_(f),z_(f)) is the location information of the referencestation. The four unknowns t_(if0), ΔT₁, ΔT₂, ΔT₃ can be calculated fromequation group (4). After ΔT_(i) is calculated, the equation group (3)can be solved and the user position can be obtained.

FIG. 2 illustrates a schematic diagram of a hybrid positioning system200 using GPS signal and/or DBS signal according to one embodiment ofthe present invention. The hybrid positioning system includes aplurality of GPS satellite (SV0 202, SV1 204, SV2 206, SV3 208), aplurality of DBS transmitters (210, 212, 214), a GPS/DBS receiver 220,an assist server 216, and a base station 218. The plurality of GPSsatellites are used to transmit GPS signals which include navigationdata. The assist server 216 is located in a clear outdoor environment.Therefore, the signal strength of the GPS signal received by the assistserver 216 is generally stronger than that of the signal directlyreceived by the receiver. Based on the stronger GPS signals, the assistserver 216 is capable of measuring a Doppler shift of each GPS satelliteand Doppler shift rate of each GPS satellite from the received GPSsignals. Then, these measured information are transmitted from theassist server 216 to the base station 218. The base station 218 iscapable of providing GPS assistance data to the receiver 220 for abetter performance of the receiver. The receiver 220 receives the GPSsignals along with the GPS assistance data and determines the userlocation. Furthermore, the assist server 216 is further capable ofreceiving the DBS signals transmitted from the DBS transmitter 0 210,the DBS transmitter 1 212, the DBS transmitter 2 214. The DBS signalsinclude DBS data indicating the coordinates of each DBS transmitter.Based on the coordinates of the DBS transmitter 210, 212, 214 and thecoordinates of the assist server 216, the transmission time difference(ΔT_(i)) can be calculated according to equation group (4). The receiver220 receives the DBS signals transmitted from each DBS transmitter andthe assistant data from the assist server 216. It is understood by thoseskilled in the art that, for the GPS system, the user position can bedetermined via the GPS signals transmitted from at least four GPSsatellites, while, for the DBS positioning system, the user location canbe determined via the DBS signals from at least three DBS transmitters.It should be noted that the number of GPS satellites and the DBStransmitters are not limited to the number shown in FIG. 2. Amodification of the number of the GPS satellites and DBS transmitterscan be conceived according to different embodiment of the presentinvention without departing from the spirit of the present invention.

The DBS/GPS receiver 220 can choose to receive signals from DBStransmitters or GPS satellites according to application environments.Assistance data is used when the receiver operates in assisted mode. Thepresent invention provides a plurality of positioning modes. Thereceiver 220 is able to switch between different positioning modesdepending on the received signal strength or working environments. Theplurality of positioning modes include stand-alone GPS positioning mode,assisted GPS (AGPS) positioning mode, assisted GPS positioning with DBSassist mode, DBS positioning with GPS assist mode, stand-alone DBSpositioning mode, and assist DBS positioning mode. The followingdescription will explain each mode in detail.

Stand-Alone GPS Positioning Mode

Stand-alone GPS positioning mode is directed to conventionalapplications under open sky and outdoor environment. The receiverrequires the GPS signals transmitted from at least 4 satellites. Thereceiver extracts the coordinate information from the four GPS signalsand determines the time difference for receiving the four GPS signals asunderstood by those skilled in the art. Thus, the user position can becalculated based on the formula given by equation group (3).

Assisted GPS (AGPS) Positioning Mode

In this mode, the receiver receives and uses the GPS signals and the GPSassistance data from the assist station (i.e. assist server 216 in FIG.2). The AGPS positioning mode utilizes assistance data from the assiststation 216 to assist the positioning in terms of acquiring and trackingstage. The GPS assistance data include Doppler shift, Doppler shift rateand navigation data. Assisted by the GPS assistance data, the receivermay perform coherent integration in a long time period and obtain ahigher gain of the spread spectrum signal. However, the use of theassistance data requires an accurate GPS time. Therefore, the receiverworking in AGPS mode must undertake a critical step: clocksynchronization. That is, the local time of the receiver must besynchronized with the GPS time before the utilizing the assistance data.One approach to realize time synchronization is to use a large quantityof parallel correlators to conduct correlation based on a certain GPSsignal. When the certain GPS signal is acquired, the receiver thenstarts to search and acquire more GPS signals from other GPS satellites.The method is severely affected by unfavorable network delay that mayoccur during the transmission of the assistance GPS data. A long networkdelay may result in a huge amount of computation task. In addition, whenthe network delay period is unknown, the time synchronization method mayalso take a lot of time. Therefore, to achieve a higher efficiency, AGPSmode requires a short network delay period and a large amount ofparallel correlators.

Assisted GPS Positioning with DBS Assist Mode

According to one embodiment of the present invention, DBS signal may beused to assist AGPS positioning by dramatically reducing the time spenton clock synchronization and thereby enhancing the performance of AGPS.For example, when the DBS signal is a DVB signal or DAB signal,synchronization time stamp (STS) information comprised in the DVB or DABsignal can be extracted from each frame. If the measurement unit of theSTS is 100 ns, it helps to determine the time when a next mega-frame istransmitted. Since the transmission distance from the DBS transmissionstation to the receiver is generally no longer than 75 Km, thetransmission delay is less than 75 Km/300,000 Km=0.25 ms. The durationcan be advantageously used to realize time synchronization in AGPS modeand consequently realize accurate and fast positioning under indoorenvironment. Assisted GPS positioning with DBS assist has outstandingadvantages over traditional AGPS in terms of TTFF (Time-To-First-Fix)performance, especially under conditions when the number of DVB/DABtransmitters are limited.

DBS Positioning with GPS Assist Mode

This positioning mode is desirable in the situation when both the numberof DBS transmitters and the number of visible GPS satellites arelimited, for instance, 2 DBS transmitters and 3 visible GPS satellites.In this case, the receiver 216 receives both DBS signals and GPSsignals. Therefore, this positioning mode is also referred to as a mixedpositioning mode. It should be noted that the total number of thetransmission stations (including DBS transmitters and GPS satellites)should be at least five stations. The reason for using at least fivestations is that the mixed employment of the two positioning systems mayintroduce a new unknown factor (the transmission time difference betweenthe two systems). Originally, in equation group (3), the locationinformation from the 4 transmission stations may help to calculate thefour unknowns x, y, z and M. However, with the introduction of the newunknown factor, one more equation is needed to calculate the additionalunknown factor. Therefore, there should be at least five transmissionstations to provide the coordinate information and the equation group(3) should be amended accordingly. The user position can be determinedby analyzing the GPS signals and DVB/DAB signal information in acomposite way.

Stand-Alone DBS Positioning Mode

In the environments such as underground parking lots and tunnels whereGPS satellites are invisible, only stand-alone DBS positioning mode iseffective. The stand-alone DBS positioning mode requires signals from atleast three DVB/DAB transmitters to conduct 2-Dimensional positioning.In this mode, no reference station is needed.

Assist DBS Positioning Mode

To improve the positioning accuracy, DBS assist station can be adoptedto provide precise clock information. Fox example, the assist stationreceives the same DVB/DAB signal and calculates the transmission timedifference ΔT_(i) based on coordinates of transmitter and assiststation. The receiver is able to obtain the reception time difference(arrival time difference) ΔT_(xi) and calculate the user informationaccording to the equation group (3).

FIG. 3 illustrates a block diagram of an exemplary GPS/DBS receiveraccording to one embodiment of the present invention. It should be notedthat the receiver is consistent with the GPS/DBS receiver 216illustrated in FIG. 2. The receiver includes a GPS RF tuner 302, a DBSRF tuner 304, a GPS/DBS assist data processing unit 306, a GPS/DBShybrid signal processing unit 308, a GPS/DBS signal detector 310, aGPS/DBS measurement data processing unit 312 and a position output unit314.

The GPS RF tuner 302 is used to receive GPS signals, convert thesesignals to GPS intermediate frequency (IF) signals, and send the IFsignals to a base band processing unit 303. The DBS RF tuner 304 is usedto receive DBS signals and convert these signals to DBS intermediatefrequency (IF) signals.

The GPS/DBS hybrid signal processing unit 308 is used to performacquisition, tracking, and demodulation of the GPS IF signal and/or DBSIF signal and to extract the navigation data or DBS data that indicatethe locating information of the corresponding transmitter. The GPS/DBShybrid signal processing unit 308 is further capable of measuring thetime difference in receiving the GPS/DBS signal (ΔT_(xi)) ( or timestamp). The GPS/DBS hybrid signal processing unit 308 outputs ΔT_(xi),and navigation data and/or DBS data corresponding to (x0, y0, z0), (x1,y1, z1), (x2, y2, z2), (x3, y3, z3) in equation group (3). The GPS/DBSmeasurement data processing unit 312 is used to solve the equation group(3) and output the user coordinates, velocity, time and other userconcerned information. The GPS/DBS signal detector 310 may detect thesignal-to-noise ratio (SNR) of received GPS and/or DBS signal. The SNRinformation is sent to GPS/DBS hybrid signal processing unit 308 and isused to determine the positioning mode as previously detailed. Based onthe SNR information, the GPS/DBS hybrid signal processing unit 308 isconfigured to operate in GPS signal processing mode (stand-alone GPSmode, AGPS mode), DBS signal processing mode (stand-alone DBS mode,assist DBS mode), or hybrid processing mode (assisted GPS positioningwith DBS assist mode, DBS positioning with GPS assist mode). Usually,each positioning mode is assigned a priority. Stand-alone GPSpositioning mode, assisted GPS (AGPS) positioning mode generally have ahigher priority.

The GPS/DBS assist data processing unit 306 may process the GPS signaland DBS signal simultaneously or process one of the two types ofsignals. In operation, the GPS/DBS signal detector 310 is able to detectwhich type of signal is stronger and choose the correspondingpositioning mode based on the detected outcome. If no DBS signal isdetected, for example, in suburban environment, the receiver will switchto the GPS signal processing mode. If the detected GPS signal is veryweak, for example, in the downtown area where high-rises are denselybuilt, the receiver will switch to the DBS signal processing mode. Boththese two modes are able to receive the assistance data from assiststation to enhance the positioning performance. It should be noted that,in one embodiment, the GPS/DBS hybrid signal processing unit 308 mayinternally include two hardware modules to process GPS IF signal and DBSIF signal independently. The GPS/DBS assist data processing unit 306 isenabled when assist modes are entered. The GPS/DBS assist dataprocessing unit 306 receives GPS assistance data and/or DBS assistancedata and outputs the processed assistance data to the GPS/DBS hybridsignal processing unit 308. The position output unit 314 outputsstandardized positioning results according to outputs from the previousstage 312.

The following descriptions of FIG. 4 through FIG. 7 are mainly focusedon how to use T-DBS signal for positioning purpose. FIG. 4 illustrates atransmission frame of a DAB signal. A DAB-T (terrestrial digital audiobroadcasting) signal is modulated using COFDM (Coded OrthogonalFrequency Division Multiplexing) approach. In the mode-I (one of the DABtransmission frame structures), the content of a broadcasting program istransmitted by 1536 carriers with 1.536M bandwidth. The audio data isencoded complying with the MPEG-II standard. FIG. 4 illustrates theframe structure of a DAB-T signal in Mode-1. Data included in the framecomes from three sources: synchronization channel, fast informationchannel (FIC) and main service channel (MIC).

FIG. 5 illustrates a detailed structure of a transmission frame of a DABsignal in Mode-I. No matter in which DAB mode, information fromsynchronization channel occupies the first two OFDM (OrthogonalFrequency Division Multiplexing) symbols. The number of OFDM symbolsrequired by the data from fast information channel and main servicechannel is related to transmission mode. For example, in Mode-I,information from fast information channel occupies three OFDM symbols,and information from main service channel occupies 72 OFDM symbols. Thedetailed frame structure is illustrated in FIG. 5. In Mode-I, eachtransmission frame is made up of 76 OFDM symbols and has a period of 96ms.

The DAB signal includes two parts: main signal s(t) and optional signals_(TII)(t) (TII refers to Transmitter identifier information). The DABsignal is the sum of s(t) and s_(TII)(t). In fact, during thetransmission time of the first OFDM symbol, s_(TII)(t) is transmitted,that is, the first OFDM symbol carries s_(TII)(t) information.

After the DAB signal is received, OFDM (Orthogonal Frequency DivisionMultiplexing) demodulation is performed. After the framesynchronization, information from synchronization channel from thetransmitter can be obtained, that is, the TII information can beextracted. After channel decoding, information from fast informationchannel from the transmitter can be obtained.

The positioning principle using DAB signal can be illustrated as below:

-   -   1. obtain TII signal. The way to obtain TII signal is described        above.    -   2. obtain Main Identifier and Sub Identifier of transmitter. The        Main Identifier and Sub Identifier correspond to the        identification number of the transmitters. A carrier pair        utilized by transmitter site can be determined from the received        TII signal. The carrier pair corresponds to parameters P and C        respectively where P equals the value of main identifier and C        equals the value of sub identifier.    -   3. obtain FIG. 0/22(Fast information group). FIG. 0/22 includes        the position information of the transmitters. The fast        information channel is divided into a plurality of fast        information block (FIB), where the fast information block is        divided into a plurality of fast information group (FIG). The        FIG. 0/22 can be obtained by filtering the FIB. When the        conditions FIG type==(000) and FIG Extension==(10110) are met at        the same time, FIG. 0/22 can be filtered out;    -   4. obtain precise position (x_(i),y_(i),z_(i)) of transmitters.        The precise position information of the transmitters that the        Main Identifier and Sub Identifier corresponding to can be        obtained from FIG. 0/22.    -   5. determine ΔT_(xi). Since each transmitter has a unique        position, the value of the main identifier and the value of sub        identifier are also unique. Consequently, the corresponding        carrier pair in TII signal is also unique. The time difference        in receiving the DAB signal (ΔT_(xi)) can be obtained through        correlation of carrier pair with locally generated carrier        signals.    -   6. calculate user position. Since (x_(i,)y_(i),z_(i)) and        ΔT_(xi) is obtained, the user position can be calculated        according to the formula given by equation group (3).        , where step 1 though 5 are performed in the GPS/DBS hybrid        signal processing unit 308 in FIG. 3 and step 6 is performed in        GPS/DBS measurement data processing unit 312 in FIG. 3.

FIG. 6 illustrates a mega-frame initialization packet (MIP) in a megaframe of a DVB signal. A DVB-T (terrestrial digital video broadcasting)signal is modulated using COFDM (Coded Orthogonal Frequency DivisionMultiplexing) approach. In 2K mode (2048 orthogonal carrier waves), datacan be transmitted by 1512 carriers with optional 6M, 7M and 8Mbandwidth. Furthermore, DVB-T may also provide support for 8K mode (8192orthogonal carrier waves). There is also a standard DVB-H similar toDVB-T, which support portable signal reception. DVB-H supports 4K mode.Bother DVB-H and DVB-T are based on terrestrial DVB system. For aterrestrial DVB SFN network, mega-frame initialization packet (MIP) isinserted into TS stream in SFN adapter. The MIP indicates the start ofthe transmission of the first packet in a mega-frame (SynchronizationTime Stamp, STS). The MIP format is shown in FIG. 6.

The format comprises a plurality of segments including transport packetheader, synchronization ID, pointer, periodic flag, synchronization timestamp, Tx identifier, etc. MIP can be filtered out based on packetheader, whose characteristic word is 0x15. Synchronization ID is used toindicate the existence of SFN network, whose characteristic word is0x00. Two-word pointer indicates the number of TS packets between twoMIP. Periodic flag (PF) indicates whether MIP message is transmittedperiodically or not. Synchronization time stamp (STS) indicates thedifference between the time when a next Mega-frame is output from singlefrequency network adapter and the standard GPS time. Tx identifierindicates which transmitter the received signal is from.

The positioning principle using DVB signal can be illustrated as below:

-   -   1. receive an OFDM signal, filter out MIP message based on        packet header after synchronization and channel decoding;    -   2. determine whether the assistant information from the        reference station is needed according to the value of        synchronization ID. If SFN network is indicated, synchronization        time stamp represents the value of ΔT_(i)(i ∈ [1,3]) in the        positioning equation group (3); otherwise, the assistant        information from reference station is needed to obtain ΔT_(i);    -   3. determine the identification number of each transmission        tower according to Tx identifier. By looking up the database,        the geographical coordinates of the transmission tower [(x₀, y₀,        z₀), (x₁, y₁, z₁), (x₂, y₂, z₂), (x₃, y₃, z₃)] can be obtained.    -   4. obtain the reception time difference (ΔT_(xi) (i ∈ [1,3])) in        receiving multi-path DVB wireless signals.

FIG.7 illustrates a frame of an ATSC signal. An ATSC signal is modulatedfollowing vestigial side band modulation rule with 8 side bands (ATSC8-VSB), and the symbol rate is 10.762237. ATSC signal is transmitted inthe format of a frame. The frame structure is illustrated in FIG. 7.Each ATSC frame is made up of 624 segments which include fieldsynchronization segments and data segments. Each segment includes 832symbols. Both types of segments have the same four symbols of segmentsynchronization header, {-1,1,1,-1}. According to the ATSC standard,segment synchronization header has a period of 77.3 us. ATSC positioningprinciple utilizes the segment synchronization header to realizepositioning. During the establishment of SFN network, in order toascertain the source of the received signal and measure the receivedsignal, an RF watermark signal is asserted in ATSC signal for thatpurpose. When ATSC 8-VSB carries RF watermark signal, the watermarksignal has two functions. One is to determine the source of the receivedsignal. The other is to measure various characteristics of the receivedsignal. The watermark signal adopts Kasami sequence. In fact, the Kasamisequence uses three-layer PN code. ATSC positioning principle makes useof this Kasami sequence and the field segment segments to realizepositioning.

The positioning principle using ATSC signal can be illustrated as below:

-   -   1. Receive ATSC 8-VSB, demodulate the ATSC 8-VSB signal, perform        Analog-to-digital conversion, perform correlation to extract        Kasami sequence;    -   2. compare the information in Kasami sequence with the        information from data base of the transmitters, and obtain the        geographical coordinates of the transmitter;    -   3. Since the SFN network ensure all transmitters to transmit        signals simultaneously, the transmission time difference is zero        (i.e. ΔT_(i)=0);    -   4. Since the information contained in field synchronization        segment from each frame is known to the receiver side, the        reception time difference (ΔT_(xi)) can be obtained by        performing correlation upon the field synchronization segment;    -   5. Since x_(i),y_(i),z_(i),ΔT_(i), and ΔT_(xi), are known, the        receiver position can be calculated based on the formula given        by equation group (3).

FIG. 8 is a flowchart illustrating a positioning method using GPS andDBS signal according to one embodiment of the present invention. Asignal detector in a receiver detects the presence of the GPS signal 802and detects the presence of the DBS signal 804. If the GPS signal isdetected, the signal detector will continue to determine the signalstrength, for example, the signal-to-ratio, of the GPS signal 806. Ifthe DBS signal is detected, the signal detector will continue todetermine the signal strength, for example, the signal-to-ratio, of theDBS signal 808. The receiver is capable to choose one positioning modeamong a plurality of positioning modes in a signal processing unit inthe receiver based on signal presence status and the signal strength ofa detected signal 810. If the GPS signal is undetectable the receiverenters a stand-alone DBS positioning mode. If the GPS signal isinvisible and an accurate positioning result is required, the receiverenters an assist DBS positioning mode. If the DBS signal is invisible,the receiver enters a stand-alone GPS positioning mode. If the DBSsignal is invisible and a good performance of the receiver is desired,the receiver enters an assisted GPS (AGPS) positioning mode. If both thenumber of GPS satellites and the number of DBS transmitters are visiblylimited, the receiver enters a DBS positioning with GPS assistpositioning mode. If the GPS signal is weak (especially when the GPSsignal is weak and the number of DBS transmitters are limited), thereceiver makes use of the DBS signal and enters an assisted GPSpositioning with DBS assist mode. The plurality of positioning modes aredescribed in previously paragraphs. Based on the chosen position mode,the receiver is capable of determining the location of the receiver 812.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described (or portions thereof, and it isrecognized that various modifications are possible within the scope ofthe claims. Other modifications, variations, and alternatives are alsopossible. Accordingly, the claims are intended to cover all suchequivalents.

1. A receiver for receiving wireless signals from transmitters tocalculate location information, comprising: a first tuner for convertinga global positioning system (GPS )signal from an original frequency to afirst intermediate frequency (IF), the GPS signal having a signalstrength; a second tuner for converting a digital broadcasting system(DBS) signal to a second intermediate frequency (IF), the DBS signalhaving a signal strength; a signal detecting unit for detecting thepresence of the GPS signal and the DBS signal, measuring the signalstrength of a detected signal and outputting a signal indicating anpositioning mode based on a measured signal strength; a hybrid signalprocessing unit in communication with the first tuner, the second tuner,and the signal detector, the hybrid signal processing unit capable ofchoosing an positioning mode among a plurality of positioning modes anddetermining a position of the transmitters and an arrival timedifference between each detected signal received at the receiver; ameasurement data processing unit coupled to the hybrid signal processingunit for determining the location information of the receiver based onthe position of the transmitters and the arrival time difference.
 2. Thereceiver of claim 1, wherein the DBS signal is a digital audiobroadcasting signal.
 3. The receiver of claim 1, wherein the DBS signalis a digital video broadcasting signal.
 4. The receiver of claim 1,wherein the DBS signal is an advanced television system committeesignal.
 5. The receiver of claim 1, further comprising an assist dataprocessing unit coupled to the hybrid signal processing unit forreceiving assistance data from an assist station and providing theassistance data to hybrid signal processing unit for further signalprocessing when an assist positioning mode is chosen.
 6. The receiver ofclaim 5, wherein the assistance data includes GPS assistance data. 7.The receiver of claim 5, wherein the assistance data includes DBSassistance data.
 8. The receiver of claim 5, wherein the plurality ofpositioning modes comprising a first assist positioning mode forproviding time synchronization information from the DBS signal to reducesynchronization time required in an assisted GPS positioning mode,wherein the hybrid signal processing unit uses GPS signal to determineposition based on the assistance data and DBS signal.
 9. The receiver ofclaim 8, wherein the plurality of positioning modes further comprisingan assisted GPS positioning mode, wherein the hybrid signal processingunit uses GPS signal to determine position based on the assistance data.10. The receiver of claim 8, wherein the plurality of positioning modesfurther comprising an stand-alone GPS positioning mode, wherein thehybrid signal processing unit only processes GPS signals.
 11. Thereceiver of claim 1, wherein the plurality of positioning modes furthercomprising a second assist positioning mode for providing GPS signal toassist DBS positioning when the transmitters transmitting the DBS signalare limited and the transmitters transmitting the GPS signal arelimited, wherein the hybrid signal processing unit uses both DBS signaland GPS signals to determine position.
 12. The receiver of claim 1,wherein the plurality of positioning modes further comprising a DBSpositioning mode, the DBS positioning mode being chosen when thepresence of GPS signals is not detected by the signal detector, whereinthe hybrid signal processing unit only processes DBS signals.
 13. Thereceiver of claim 7, wherein the plurality of positioning modes furthercomprising an assist DBS positioning mode, wherein the hybrid signalprocessing unit uses DBS signals to determine position based on theassistant DBS signal.
 14. A positioning method using global positioningsystem (GPS) signal and digital broadcasting system (DBS) signal,wherein GPS signal having a signal strength and DBS signal also having asignal strength, comprising: detecting a presence status of the GPSsignal through a signal detector in a receiver; detecting a presencestatus of the DBS signal through the signal detector; determining thesignal strength of the GPS signal if the GPS signal is detected;determining the signal strength of the DBS signal if the DBS signal isdetected; choosing one positioning mode among a plurality of positioningmodes in a signal processing unit in the receiver based on signalpresence status and the signal strength of a detected signal; anddetermining a location of the receiver based on the chosen positioningmode.
 15. The method of claim 14, wherein the DBS signal comprises adigital audio broadcasting signal.
 16. The method of claim 14, whereinthe DBS signal comprises a digital video broadcasting signal.
 17. Themethod of claim 14, wherein the DBS signal comprises an advancedtelevision system committee signal.
 18. The method of claim 14, furthercomprising providing assistance data to enhance positioning performanceof the receiver.
 19. The method of claim 18, wherein the assistance datacomprises GPS assistance data.
 20. The method of claim 18, wherein theassistance data comprises DBS assistance data.
 21. The method of claim18, wherein the plurality of positioning modes comprises a first assistpositioning mode for providing the receiver a time synchronizationinformation from the DBS signal to reduce synchronization time requiredin an assisted GPS positioning mode, wherein the receiver uses GPSsignal to determine position based on the assistance data and DBSsignal.
 22. The method of claim 18, wherein the plurality of positioningmodes further comprising an assisted GPS positioning mode, wherein thereceiver uses GPS signal to determine position based on the assistancedata.
 23. The method of claim 18, wherein the plurality of positioningmodes further comprising a stand-alone GPS positioning mode, wherein thereceiver only receives GPS signals.
 24. The method of claim 14, whereinthe plurality of positioning modes further comprising a second assistpositioning mode for providing GPS signal to assist a DBS positioningmode when the number of transmitters transmitting the DBS signal arelimited and the number of transmitters transmitting the GPS signal arelimited, wherein the receiver uses both DBS signal and GPS signals todetermine position.
 25. The method of claim 14, wherein the plurality ofpositioning modes further comprising a DBS positioning mode, the DBSpositioning mode being chosen when the presence of GPS signals Is notdetected by the signal detector, and wherein receiver only processes DBSsignals.
 26. The method of claim 20, wherein the plurality ofpositioning modes further comprising an assist DBS positioning mode,wherein the receiver uses DBS signals to determine position based on theassistant DBS signal.